Field of the Invention
The present invention relates to a charging/discharging control circuit and a charging/discharging control device capable of controlling charging/discharging of a secondary battery, and a battery apparatus equipped with the charging/discharging control device.
Background Art
As a related art battery apparatus equipped with a charging/discharging control device, there has been proposed one equipped with a power-down circuit which suppresses a further voltage drop of a secondary battery where the secondary battery becomes an overdischarging state in which the voltage of the secondary battery is lower than a prescribed voltage (refer to, for example, Patent Document 1). According to such a power-down circuit, it is possible to reduce current consumption of the charging/discharging control device itself.
In such a related art battery apparatus, when secondary batteries equivalent to the number exceeding the breakdown voltage of the charging/discharging control device are connected in series, it follows that a plurality of charging/discharging control devices are arranged.
FIG. 3 illustrates a circuit diagram of a battery apparatus 300 according to a related art, which is equipped with a plurality of secondary batteries.
The related art battery apparatus 300 is equipped with external terminals 401 and 402 between which a charger or a load is connected, two secondary batteries 403-1 and 403-2 connected in series between the external terminals 401 and 402, a discharging control switch 404, a charging control switch 405, and charging/discharging control circuits 301-1 and 301-2 respectively connected to the secondary batteries 403-1 and 403-2.
The charging/discharging control circuit 301-1 is configured so as to be equipped with a battery voltage monitoring circuit 30-1, an output control circuit 31-1, and a power-down circuit 33-1. Likewise, the charging/discharging control circuit 301-2 is configured so as to be equipped with a battery voltage monitoring circuit 30-2, an output control circuit 31-2, and a power-down circuit 33-2.
The charging/discharging control circuit 301-1 is operated as follows:
The battery voltage monitoring circuit 30-1 monitors the voltage of the secondary battery 403-1 and outputs a detection signal indicating that the secondary battery 403-1 is in an overdischarging state or an overcharging state to the output control circuit 31-1. When the detection signal indicating that the secondary battery 403-1 is overdischarged is outputted, the output control circuit 31-1 turns OFF the discharging control switch 404. When the detection signal indicating that the secondary battery 403-1 is overcharged is outputted, the output control circuit 31-1 turns OFF the charging control switch 405. The power-down circuit 33-1 outputs a power-down signal to the battery voltage monitoring circuit 30-1 in response to an overdischarge signal ODC-1 generated on the basis of the fact that the secondary battery 403-1 is overdischarged and the discharging control switch 404 is turned OFF. Further, when the battery voltage monitoring circuit 30-1 receives the power-down signal outputted from the power-down circuit 33-1, the battery voltage monitoring circuit 30-1 stops its own operation. Thus, current consumption of the charging/discharging control circuit 301-1 is reduced.
Since the operation of the charging/discharging control circuit 301-2 is similar to that of the charging/discharging control circuit 301-1, its description will be omitted.
A description will next be made about the generation of the overdischarge signals ODC-1 and ODC-2 for generating the power-down signals in the power-down circuits 33-1 and 33-2 respectively.
The battery apparatus 300 is further equipped with Nch transistors 310, 311, 316, and 317, Pch transistors 312, 315, 318, and 320, resistors 314, 319, 321, and 322, and a Zener diode 313, which are connected between the external terminals 401 and 402.
When the secondary battery 403-1 is overdischarged and the discharging control switch 404 is turned OFF, the voltage of the external terminal 402 is operated so as to be equal to that of the external terminal 401 by a load (not illustrated) connected between the external terminals 401 and 402. That is, when the voltage of the external terminal 402 rises. When the voltage of the external terminal 402 rises, the Nch transistor 311 and the Pch transistor 315 are turned ON, the Nch transistor 316 is turned OFF, and the Pch transistors 310 and 312 are turned OFF. Thus, the overdischarge signal ODC-1 is pulled up to the positive power supply voltage of the secondary battery 403-1. Further, since the Nch transistor 317 is turned OFF, the Pch transistor 318 is turned ON, and the Pch transistor 320 is turned OFF, the overdischarge signal ODC-2 is pulled up to the positive power supply voltage of the secondary battery 403-2.
Further, since each transistor is operated in the same way as when the secondary battery 403-1 is overdischarged, even when the secondary battery 403-2 is overdischarged, the overdischarge signal ODC-1 is pulled up to the positive power supply voltage of the secondary battery 403-1, and the overdischarge signal ODC-2 is pulled up to the positive power supply voltage of the secondary battery 403-2, respectively.
In the related art battery apparatus as described above, even if any of the plural secondary batteries is overdischarged where the plural secondary batteries are connected in series, the respective power-down circuits of the plural charging/discharging control circuits are operated to make it possible to reduce current consumption.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-229774